I received the headlight harness from Icejawa and went through it today: there was nothing wrong. I did check for cross-feeds on any headlight-related lines and found nothing.
There was a single sportslamp bulb, of unknown number. The proper bulb is 96. In all of the discussions in this thread, the sportslamps never came up, but they are powered whenever the headlight switch is pulled out. I wonder...
I provided some additional trouble-shooting ideas for why the engine bogs down when the headlights come on. Basically, remove sportslamps, then headlamps, then side-marker lamps, then tail-lights one at a time to see which system is causing the problem.